New piston forgings for GM 305 small blocks

• Forged rib-side design with strongest known stiffening ribs
• Supplied with 4130 alloy steel piston pins case hardened to 60 Rockwell

Clinton Township, MI: Diamond has announced a new forged piston for all 305 GM small-block engines including the 305 RaceSaver Sprint cars.

25dSBC305FTSeriesCreated in a flat-top style with two symmetrical valve pockets 2cc deep, these new pistons are constructed from resilient 2618 alloy and thus street cars can accept small applications of nitrous oxide if desired. Lower skirt rigidity is maintained by a rib-side design that boasts the strongest known stiffening ribs, located just below the piston pin bores. Robust ribs promote piston strength and combat heat and pressure. Moreover the rib-side concept is lighter than its counterpart the full-round style.

Beyond this, Diamond provides tough 4130 alloy steel piston pins 0.927 x 2.750in and case hardened to 60 Rockwell C. To lubricate the pins, double oiling ports are featured in each pin bore, which are fed from the oil control ring groove.

Prepared for bore sizes measuring 3.766in to 3.796in., piston ratios are configured on the customary 9in deck height with the piston set at 0.010in below. The top ring groove is positioned 0.200in down from the piston crown. Between the first and second ring lands a pressure balance groove is provided to relieve excessive pressure and therefore maintain reliable ring seal. Piston ring packs are available separately; they comprise 1/16in x 1/16in x 3/16in.

For more information contact:
Diamond Pistons 23003 Diamond Drive, Clinton Township, MI 48035

Telephone (877) 552-2112 or visit or e-mail Mike Knowles at

Editors’ Contact: Victor Moore (706) 531-0058 or